Facile ACQ-to-AIE transformation via diphenylphosphine (DPP) modification with versatile properties

Aggregation-induced emission (AIE) materials have attracted increasing research attention due to their broad application potential. The major design strategy for AIE luminogens (AIEgens) is incorporating molecular rotors, such as tetraphenylethylene (TPE) and triphenylamine (TPA), into conjugated skeletons to decrease intermolecular pi-pi interactions. Therefore, the diversity of AIEgens is usually determined by the types of molecular rotors. Herein, we report a new molecular rotor, diphenylphosphine (DPP), that can be incorporated facilely into a typical aggregation-caused quenching (ACQ) luminophore to facilitate ACQ-to-AIE transformation. Due to the large steric hindrance and sp(3) hybrid conformation of diphenylphosphine, the intermolecular pi-pi interaction is limited to a certain extent; the photoluminescence quantum yields of our AIEgens range from 10.3% to 47.0%. Furthermore, the luminescent color of the molecules can be tuned from blue to orange by adjusting the electron-donating/withdrawing strength of the substituent groups. At the same time, the AIEgens also exhibit novel pressure-induced emission enhancement (PIEE) properties. The rapid intersystem crossing (ISC) process was explored as the DPP-based AIE mechanism by ultrafast IR spectroscopy. To our best knowledge, this is the first systematic study of a general strategy to realize ACQ-to-AIE transformation by using the DPP group, which greatly increases the diversity of AIEgens as well as their potential applications.